ET: Engine (Twin) Primary side main bearings

Bill Thomas

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I agree David, But we have to do the best with what we have.
To me it's a Miracle our Bikes are still going well.
For me it was a mistake to change from the "A" type Mains.
I got fed up with Bodging mine with Loctite, Which didn't work !,
I was Sprinting and Road Racing for 10 years, So I was a bit hard on Poor Old Girl !.
So I took the cases to a Top Man, Another Mistake !!.
We took a Comet Engine apart some time ago, I don't think the Comet has as bad a problem as the twin's,
Because the Crank is more narrow.
But we could not get the outer main out !!, No matter how hot we got the cases.
Turned out the owner before, Ground some "Huge" flats on the outer track and bashed the alloy over them !.
 

BigEd

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Is it only me who likes the Lipped outer race for the inner main bearing ?.
Our "A" Man told us about many years ago,
They can't walk out !!.
Like all Mod's it needs some playing around, I helped fit them to Big Bill Telfer's a long time ago and
Have a set for my new Comet.
I am pretty certain that when I had a new big-end in my Rapide the drive side mains were fitted with the lipped mod so that they can't move. I'm not planning on having a look any time soon. (Fingers firmly crossed.)
 

Martyn Goodwin

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From MPH 567 and found in Another 10 Years

Main bearing 001.jpg


Main bearing 002.jpg
 

Bill Thomas

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I think you can only get the bearings "Full width " ?,
So have to get the outer ring ground more narrow for the Vin',
The grinding may make the track "Magnetic ", So that has to be reversed or it could cause problems ?.
I can't remember if both the bearings should be narrow or just the drive side where the alloy spacer and oil scroll goes ?.
 

roy the mechanic

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Timken main bearings are not a new idea. H-D have been fitting them since at least 1936. They are fit and forget. A well known vin racer(name witheld) has used them with 100% satisfaction. When asked he said"Ihave to use them as I run oversized mainshafts". I am yet to be convinced about the clearance as H-D manuals give 3-4 thou nip. Like in a car differential pinion bearings.
 

roy the mechanic

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I figure the scroll would be the start of the spacer, main seal makes sense, watch out, I bought the seal and motor sprocket from the same supplier, had to machine a bit from the inside of the sprocket to stop it binding on the fixing screw heads|
 

Robert Watson

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20180122_142403_HDR.jpg


These main bearing outer races don't move. That's on top of .002 interference.

Also I meant to mention in my recent post about tapered roller mains. They were in the engine when I assembled the rest of the machine. After startup it went 100 miles and had a catastrophic failure. The bearings were made by Bower and the steel cages which separate the rollers were defective, they were cut 95% through at one end. One got caught by the bearing and rolled the whole cage up into the rollers. We only know this because the other one had not failed and is to this day sitting on my bench to remind me to check parts you get from even the most reliable sources. It was then i did a lot of research on fitting them with .003 crush. I talked with bearing suppliers, manufacturers reps and a lot of experienced people. Answers ran the whole gamut from "no wonder your bearings disintegrated" to .003 is not enough. In the end I settled on .003. That was some 120,000 miles ago. I don't worry about it any more.
 

Cyborg

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VOC Member
I think you can only get the bearings "Full width " ?,
So have to get the outer ring ground more narrow for the Vin',
The grinding may make the track "Magnetic ", So that has to be reversed or it could cause problems ?.
I can't remember if both the bearings should be narrow or just the drive side where the alloy spacer and oil scroll goes ?.

You can still get the narrow bearings or you can use the wider ones with a narrow ET77 and ET19 or you can take the wider bearing race and just chuck it in the lathe. Leaves a nice finish.

Bearing narrowing.jpg
 
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